1. Field of the Invention
The present invention relates to finishing processes after heat treatment of cylindrical gears.
More specifically, the invention relates to a power honing/grinding machine for the finishing of cylindrical gears with external toothing tools.
2. Description of the Related Art
A power honing machine of the known type comprises a workpiece clamping unit having a first electrospindle rotatable about a first axis, and a tool-holder unit having a second electrospindle rotatable about a second axis, wherein the movement of rotation of the second electrospindle about the second axis is synchronized with the movement of rotation of the first electrospindle about the first axis.
The honing process with synchronized axes and high removal of material is usually carried out on machines that use ceramic tools with internal toothing working on the principle of intersecting axes. The use of tools with internal toothing poses physical limits to the degree of intersection of the axes. In fact, the meshing of a gear with external toothing with a tool with internal toothing poses limits on the angle of mutual inclination between the respective axes of rotation. In practice, with the known solutions, employing tools with internal toothing values of 15-20° of inclination of the axes are not exceeded. Since the axial cutting speed is proportional to the sine of the angle of intersection of the axes, the limitation of the angle of intersection of the axes penalizes the axial cutting speed.
If an increased cutting speed is desired, without reaching prohibitive values of the gear clamping spindle speed, it is necessary to use tools with external toothing. External toothing tools do not limit the angle of intersection of the axes. With external toothing tools it is possible to reach intersection angles of the axes equal to 60°.
However, practical tests have shown that the use of external toothing tools in machines with electronic synchronization between the tool-holder spindle and the gear clamping spindle creates great problems of finishing quality. Indeed, disturbances in the rotation of one spindle have repercussions on the other spindle, sometimes triggering phenomena of self-maintenance of perturbations.